KR102586409B1 - Coating by ALD to suppress metal whiskers - Google Patents

Abstract

A deposition method is provided that includes depositing a stack on the surface of a substrate by atomic layer deposition (ALD). Also provided are an ALD reactor for carrying out this deposition method and products obtained using this deposition method.

Description

Coating by ALD to suppress metal whiskers

The present invention generally relates to atomic layer deposition techniques in which materials are deposited on the surface of a substrate.

This section illustrates useful background information, without acknowledging that any of the techniques described herein represent prior art.

Atomic Layer Deposition (ALD) is a specialized chemical vapor deposition method based on the sequential introduction of at least two reactive precursor species to at least one substrate in a reaction space. Plasma enhanced ALD (PEALD) is an ALD method in which additional reactivity to the substrate surface is delivered in the form of plasma-generated species. Additionally, a related process is Atomic Layer Etching (ALE), a type of inverted ALD, in which the conformal removal of one, possibly specific, atomic or molecular layer is achieved with the help of specific chemistries. ) is accomplished. Additionally, a subclass of ALD is Molecular Layer Deposition (MLD), which refers to depositing more than one atom per layer at a time, which in many cases includes organic materials. Such materials are discussed in “Beilstein J. Nanotechnol. 2014, 5, 1104-1136” (Organic and inorganic-organic thin film structures by molecular layer deposition: A review, Pia Sundberg and Maarit Karppinen).

In ALD processes, substrates are usually not cleaned because they are transferred from other clean processes or from clean substrate boxes to the ALD tool in a clean room. The molecular layer absorbed from the air or ambient is usually relieved by heating the commonly used silicon wafer substrate to a temperature of up to 300° C. in a flow of inert gas. In contrast, conventional reflow or manual soldering steps leave some traces of flux, which is detrimental to ALD deposition. Additionally, PCBs, for example, do not tolerate such high temperatures as silicon wafers do and require different cleaning.

Metal whisker formation is a problem encountered especially when using metals and metal alloys (e.g., Sn and Sn alloys, Cd and Cd alloys, and Zn and Zn alloys). Metal whiskers include metal spikes or other irregularities on the surface that can short-circuit, corrode, induce corrosion, or increase unwanted particle accumulation (as a result of increased surface area). and changes the RF performance of RF-lines and components. Meanwhile, corrosion has generally been mentioned as an important factor in the tendency for whiskers to occur. Metal whisker formation can begin, for example, in the soldering process of printed circuit boards (PCBs), upon electroplating of electronic components or boards (also known as reflow of solder paste), even after several years. Even later, regardless of the conditions in which the PCB was stored or used, problems can occur.

The problem of metal whisker formation is also critical in the case of electronic circuits, but is also relevant for, for example, components used in electronics and electronics cases (which are often made of electroplated metal).

In particular, tin whisker formation has previously been significantly reduced by adding Pb to the alloy. However, due to the toxicity of Pb, new methods are needed to mitigate or ultimately prevent tin whisker formation and possibly also improve corrosion protection. In particular, the formation of filament-like tin whiskers in PCBs and electronic components can cause problems, and therefore there is a need to prevent their formation.

In the literature, various factors affecting the formation of tin whiskers have been suggested. Such factors include: surface tension; temperature; humidity; electric potential; electrostatic charge; and imperfect metal surfaces due to structural defects, oxide layers, grain boundaries, ionic contamination, local stresses and stress gradients. Some of these details are discussed in the recently published Journal of Applied Physics 119, 085301 (2016), Surface parameters determining a metal propensity for whiskers, Diana Shvydka and V. G. Karpov.

According to a first aspect of the present invention, a deposition method is provided that reduces metal whisker formation, electromigration, and corrosion, the deposition method comprising:

providing a substrate;

Pretreating the substrate by washing;

pretreating the substrate by preheating and/or evacuating; and

and a stack deposition step including depositing at least the first layer 100 by atomic layer deposition (ALD).

According to a second aspect of the invention, there is provided the use of the method of the first aspect for protecting a substrate from metal whisker formation, electromigration and/or corrosion.

According to a third aspect of the invention, there is provided an ALD reactor system (700) comprising control means (702) configured to cause the ALD reactor system to perform the method of the first aspect. do.

According to one aspect, a device is provided comprising a substrate deposited using the method of the first aspect.

Various non-binding example aspects and implementations of the invention have been described above. The above implementation examples are merely used to describe selected aspects or steps that may be used in implementing the invention. Some implementations may be presented with reference only to specific illustrative aspects of the invention. It should be understood that corresponding implementations may apply to other example aspects as well. Any suitable combination of embodiments may be formed.

Hereinafter, the present invention will be described by way of example only with reference to the accompanying drawings.
1 shows a flow diagram of a method according to an example implementation.
Figure 2 shows a schematic diagram of implementations of a stack deposited on a substrate deposited using the present method.
Figure 3 shows an ALD reactor system according to an example embodiment.
Figures 4A and 4B are SEM images showing reduced filament whisker formation on a SnAg sample coated using the method of the first aspect (Figure 4A) compared to an uncoated control sample (Figure 4B). The uncoated substrate in Figure 4b shows filamentous whiskers with a length of several tens of μm. The scale bar in FIG. 4A is 10 μm, and the scale bar in FIG. 4B is 20 μm.

In one implementation, the stack deposition step includes a first pulse starting with at least one reductive chemical.

In one implementation, the stack deposition step includes a first pulse starting with at least one oxidizing chemical.

In one implementation, the stack deposition step includes a first pulse consisting of multiple pulses of the reducing chemical or chemicals with subsequent inert gas pulses therebetween.

In one embodiment, the metal includes Zn, Zn alloy, Sn, Sn alloy, Cd or Cd alloy, or Ag or Ag alloy.

In one embodiment, the substrate includes or is a printed circuit board (PCB). The substrate may be commonly known as an assembled PCB or PCB assembly with components, but is referred to herein as a PCB. However, as should be noted, this process is suitable for semi-finished products (e.g. PCB boards or PCBs with solder paste, or PCBs with reflowed solder, electronics assemblies or sub-assemblies). ) is applicable to In other embodiments, the substrate is a component, component housing, metal package, or metal housing. Additionally, repair or refurbishment can also be performed by the ALD coating described herein. In one embodiment, the deposition processes described above and described hereinafter form a manufacturing step for an electronic product.

Additionally, components that may be used as part of the electronics of a PCB or electronics assembly may have a metallization coating or metal package, which may include metal whiskers. can be formed. Such coating methods include commonly known “immersion tin” and the like. The method also applies to such substrates.

The method, in one embodiment, is used to protect substrates such as electronic components and electronic circuits, including PCBs. The method and its use are particularly useful in applications where quality and environmental resistance are particularly important (e.g., electronics intended for use in aerospace, medical, industrial, automotive and military fields).

In one implementation, first layer 100 includes a layer of at least one ALD layer. The first layer is optionally applied to adhere to the substrate 10. In one embodiment, adherence is most optimal.

In one implementation, the stack further includes depositing the second layer 200 by atomic layer deposition (ALD).

In one implementation, second layer 200 includes numerous sublayers. In one embodiment, at least one lower layer is an elastic layer.

In one implementation, second layer 200 consists of at least one elastic layer.

In one implementation, the second layer 200 is comprised of at least one organic layer or a layer containing silicone polymer.

As an example, layer 200 is n×(I + II), where n ≥ 1, I consists of at least two chemicals (e.g., TMA + H ₂ O), and II is: At least one of them is any other combination of chemicals from layer I and other chemicals. Additionally, any other combination (e.g. n*(I + II + III) or n*(I + II) + m*(III + IV) or x{n*(I + II) + m*( III + IV)}, where m≥1) can be used. Each of I, II, III and IV consists of two chemicals, wherein at least one of them is different compared to each other and optionally different compared to those used in I and II.

In one implementation, the stack further includes depositing a third layer 300 by atomic layer deposition (ALD).

In one implementation, third layer 300 is the top layer.

In one embodiment, pretreating the substrate by washing includes cleaning by washing.

In one embodiment, pretreating the substrate by cleaning includes cleaning with a solvent.

In one embodiment, pretreating the substrate by cleaning includes cleaning by blowing or cleaning by a non-liquid fluid such as a gas or gases.

In one embodiment, pretreating the substrate by preheating includes preheating with a pulse of heated gas having a temperature greater than the reaction temperature.

In one embodiment, any one of sublayers I, II and III independently comprises an electrically insulating material.

In one embodiment, layer II is an organic layer.

In one embodiment, layer II is an organic or silicone polymer containing layer.

In one embodiment, layer III is an organic or silicone polymer containing layer.

In one embodiment, at least one of layers I, II, III and IV comprises a reactive chemical that is reactive with the ambient.

In one embodiment, at least one of layers I, II and III is a hard layer.

In certain embodiments, any of layers I, II, and III; Layer IV and Layer IV are independently selected from ALD layers, electrically insulating layers, oxides, carbides, metal carbides, metals, fluorides and nitrides (these layers include molecular layers deposited by molecular layer deposition (MLD)). .

In one embodiment, layer II is a MLD deposited layer (thereby effectively depositing multiple atoms at a time) (e.g., an organic layer (e.g., Alucone or Titanicone) ), or a layer containing various different atoms (e.g., C, N, Si and/or O). In a further embodiment, this layer forms polymer chains or cross-links, enabling commonly known mechanical strength or formation. Known examples of such cross-linked polymer structures are aliphatic polyureas, hexa-2,4-diyne-1,6-diol with DEZ and TiCl ₄ , and silicone polymers -(SiR ₂ -O))n-. In one embodiment the effect of polymerization includes the combined effect via UV-polymerization, in an ALD reactor, in a vacuum cluster or outside the assembly.

In one embodiment, layer II is an organic or silicone polymer chain-containing layer. Layer II is preferably resistant to cracking and allows deformation of the deposited layers. In one embodiment, layer II is a cross-linked layer. In another embodiment, layer II is a single layer or comprises multiple molecular layers. Accordingly, multiple layers of Layer II can be deposited to provide a thicker laminate with elastic behavior similar to the overall stack. Such layers are particularly advantageous for maintaining corrosion resistance by providing resistance to cracking (eg, caused by Hillock, or similar small formations in the first layer or stack).

In one embodiment, the thickness of the stack is 1 to 2000 nm, preferably 50 to 500 nm, most preferably 100 to 200 nm.

In one embodiment, the method further includes altering, stopping or limiting fore-line exhaust flow. In one implementation, changes, stops or limits are synchronized with chemical pulses.

In one embodiment, the method further includes providing an additional coating on top of the stack by an additional coating method.

In one embodiment, the additional coating includes a polymer such as lacquer or a silicone polymer.

In one embodiment, the additional coating comprises, for example, providing (or, for example, dip-coating) a lacquer, etc. to the substrate.

In one embodiment, the additional coating includes providing a conventional organic or silicone polymer coating applied by conventional means (eg, spraying, brushing or dip-coating).

In another embodiment, in addition to or instead of layer II, a layer comprising carbon nanotubes, a carbon nanotube network, or a graphene network is provided in the stack. In one embodiment, such layer is covered, in one embodiment on all sides, with a layer of electrically insulating material (eg Al ₂ O ₃ ). In another embodiment, the carbon nanotubes or carbon nanotube nets are configured to be electrically insulating.

In one embodiment, the method further deposits, instead of or in addition to the second layer 200, a layer comprising at least one sublayer comprising carbon nanotubes, a carbon nanotube network, or a graphene network. It includes steps to:

In one embodiment, the sublayer comprising carbon nanotubes, carbon nanotube networks, or graphene networks is coated with an electrically insulating material.

In one implementation, layer 300 is a top layer that prevents hydrolysis, such as hydrolysis by the wafer or moisture. In one implementation, layer 300 is a barrier layer. In another implementation, layer 300 includes Nb ₂ O ₅ . In another embodiment, layer 300 includes an additional material that is resistant to hydrolysis (eg, TiO ₂ , etc., or an MLD layer comprising an organic layer, eg, a fluoropolymer). In one embodiment, the thickness of the top layer ranges from 1 atomic layer to 20 nm, or from 1 to 20 nm.

In one implementation, layer 300 is a top layer configured to chemically adhere to a coating applied after an ALD process.

In one embodiment, the stack includes a hard layer instead of or in addition to layers I, II and/or III. In one embodiment, the hard layer includes a metal oxide layer. In further embodiments, the hard layer, single or in repeated stacks, is Al ₂ O ₃ , TiO ₂ , Ta ₂ O ₅ , ZrO ₂ , SiO _{2 ,} Nb ₂ O ₅ , WO ₃ , HfO ₂ , or these. are selected from combinations. Preferably, the hard layer is an Al ₂ O ₃ /TiO ₂ repeating stack, ie a repeating stack, such as a laminate.

In one embodiment, at least one of layers I, II, and III of deposited layer 100 or 200 includes a reactive chemical that is intentionally left in excess proportion within the structure. Alternatively, the oxide material can be reduced to reduce the oxygen content. The reactive chemical provides at least a partially self-healing layer. The reactive chemicals, in one embodiment, are selected from chemicals that react with ambient air or moisture. In one embodiment, the reactive chemical includes, for example, TMA, or reduced Mg or Ti.

In one embodiment, at least one of the layers includes at least one reactive chemical that is reactive with the ambient.

In one embodiment, at least one of layers I, II and III is a hard layer.

In one embodiment, the substrate includes Sn. Deposition on Sn-containing substrates is particularly advantageous because tin whisker formation can be at least partially prevented. Additionally, in one embodiment, the substrate comprises Ag, which is typically used in hybrid electronics, and which also benefits from tin whisker protection along with preventing electromigration that easily occurs.

In one embodiment, the method is a high aspect ratio (HAR) ALD coating, e.g., pores to fill defects or cavities between layers of different materials or beneath components on a PCB. It includes performing coating (pore coating). This is desirable in the case of polymer packages or when depositing interfaces between different materials of a PCB (eg, interfaces between metals and other materials used in PCB construction). In one implementation, high aspect ratio deposition is performed at a temperature below the maximum deposition temperature. This is desirable for coating pores that close at high temperatures due to thermal expansion.

In one embodiment, the fore-line flow is modified by known processes, or stopped flow or restricted flow (known as PicoFlow) is used to achieve significantly increased aspect ratio coating in the cavity. It is used to enable a coating to obtain and to obtain increased uniformity of the coating.

In one embodiment, when depositing on substrates containing certain polymers (which may absorb reactive chemicals or their metals or ligands), low temperature processes may be used throughout the entire process or at the start of the process. For example, temperatures below 50° C. are used to deposit diffusion barriers for higher temperature (and therefore faster) deposition.

In one embodiment, the total thickness of the deposited stack is sufficient to provide mechanical, chemical and electrical insulating properties to the substrate. In one embodiment, the height of the stack is 1 to 2000 nm, preferably 50 to 500 nm, most preferably 100 to 200 nm. In one embodiment, the process includes preheating and cleaning of the substrate, followed by deposition of at least one atomic or molecular layer conformally with ALD.

In one embodiment, the process temperature of deposition is selected to correspond to the maximum temperature that the substrate can withstand. In one embodiment, the process temperature is not the maximum temperature, but a temperature below that maximum temperature. For PCBs for aerospace applications, the process temperature can be 125 °C. In another embodiment, the process temperature is above the boiling point of water at the selected pressure, thereby preventing absorption and condensation at the surface.

In one embodiment, the substrate is a PCB and the method includes a soldering step at a temperature above the solder melt temperature, also known as reflow. This is advantageous in providing a bubble-free structure in the solder, or when manufacturing PCBs in a vacuum.

In one embodiment, the processing temperature is lower than the soldering temperature, but with the help of the ALD process, the soldering effect occurs in such a way that the soldering particles or spheres adhere together. This can additionally apply to adherence to substrates and to components. Additionally, a soldering step is performed after the ALD process, either inside or outside of the ALD tool, although the ALD process may be insufficient to produce final attachment via solder.

In one implementation, the substrate is partially masked prior to deposition to provide openings in the deposited stack.

In one implementation, a stack of the desired thickness can be deposited directly on the substrate. Stack layers are deposited in the same ALD reactor or in additional ALD reactor(s).

Depositions of the stack can form manufacturing steps for a product, or can be integrated to become part of a production line.

1 shows a flow chart of a method according to one embodiment of the present invention. In Step 1, a substrate intended for deposition is provided. The description includes those described above and as will be described later. In Step 2, the substrate is pretreated (e.g., washed, cleaned, or preheated) prior to inserting or loading the substrate into the ALD reactor or after the substrate is inserted into the ALD reactor.

Both PEALD and ALD processes can be used to clean the surface prior to coating, using a plasma of PEALD chemicals or using a gaseous chemical or multiple chemicals applicable to the ALD process.

In one embodiment, pretreatment of the sample includes various steps to clean the sample (e.g., washing with a solvent or blowing) prior to inserting the sample into the ALD reactor. In one embodiment, the fluid used for cleaning is selected depending on the purpose of the cleaning (eg, removing ionic contamination and/or loose particles such as dust).

In addition to cleaning in the ALD reactor, additional surface cleaning methods include cleaning with hard Lewis acids or hard Lewis bases. In one embodiment, cleaning includes cleaning using, for example, NH ₃ , HMDS, H ₂ , O ₂ , O ₃ and/or TMA. In a further embodiment, cleaning is carried out with the aid of PEALD, where the plasma of PEALD allows for even more effective cleaning.

In one embodiment, cleaning includes using heated H ₂ or O ₂ or O ₃ .

Additionally, in one embodiment, reductive cleaning is performed using H ₂ or in the gas phase (particularly in ALD processes) with a similar effect (2-methyl-1,4-bis(trimethylsilyl)-2,5-cyclo This is done using chemicals with the same effect as reported for hexadiene or 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine.

Accordingly, in one embodiment, cleaning is achieved by a process of stabilizing the surface and providing a reducing gas pulse following the stabilization, wherein the pulse includes, for example, H ₂ , a H ₂ -containing plasma, SO ₃ , Or it may include Al(CH ₃ ) ₃ . This is referred to herein as the starting pulse, which is effectively the first pulse of reactive material released into the reaction chamber after stabilization. Additionally, to enhance the effect, it is preferred that the reducing chemical pulses follow each other at intervals (once after a delay of at least 0.01 seconds). More preferably, the reducing chemical pulses are repeated at least five times, with a delay of 5 seconds between them, after which a chemical reaction is added on the resulting surface to increase the material in ALD conditions.

In one implementation, cleaning includes ALE pulses. In one embodiment, Atomic Layer Etching (ALE) is used as an alternative to or in addition to cleaning, thereby removing impurities from the surface or, preferably, from crystal boundaries with a specific molecular composition. can be etched. In the ALE process, only preferred chemicals are removed from the surface, possibly selectively and possibly in at least two stages of cycles as reversed ALD.

After the sample is inserted into the ALD reactor, in one embodiment, additional pretreatment steps (e.g., an “in-situ” cleaning step) are performed. In one embodiment, the pretreatment includes cleaning the surface by low temperature combustion (e.g. with O ₂ , O ₃ or H ₂ ) at low temperature (e.g. 125° C.), or by reducing the temperature of the reactor space. Includes surface cleaning using higher temperature gases. In one embodiment, pretreatment includes rinsing at various pressures and temperatures using inert or chemical gases. In one embodiment, the surface is exposed to a pulse of heated gas (eg, “combusted,” oxidized or reduced), or a chemical reaction is induced on the top surface.

Heated gases are used to provide a heat treatment to a surface material (i.e., to the top layer in the micro- or nanometer thickness range of the surface material) such that such surface material could not otherwise withstand prolonged exposure to elevated temperatures. There won't be. Additionally, by using heated gas pulses, heat treatment can be applied only to the surface, which is desirable when using heat-sensitive substrates. Additionally, the outer layer of solder, in one embodiment, is remelted in this manner without damaging or separating the components. This results in an annealing effect that can affect the alloy crystals in a similar way to the steel manufacturing steps. In one embodiment, the temperature increase of the entire substrate is below the actual melting temperature of the metal.

In one embodiment, the heat pulse is performed by providing the heat pulse for a specific time, such as 0.01 to 100 seconds, depending on the gas used, reaction chamber temperature, gas flow rate used, and other gas flow rates. In another embodiment, the temperature of the heat pulse gas is raised by a heated gas introduction configured to heat the gas to a high temperature, for example 1,000°C. The pulsed mass flow, in one embodiment, is smaller (e.g., 0.1 to 50 sccm), or equivalent (e.g., 20 to 20 sccm) compared to the other gas flow or flows entering the reactor at that time. 500 sccm), or significantly larger (e.g., 200 to 20,000 sccm). Such different temperature gas flows, in combination or individually, are, in one embodiment, used to uniformly cool the coated materials, thereby allowing, individually or in combination, surface metallurgical modification of the coated materials. Let it be done. This is commonly known in the field of steel processing, but it is a bulk case and therefore dependent on the metal used. This results in a similar annealing effect, which can affect the alloy crystals in the same way as in the steel manufacturing stage.

Additionally, in one embodiment, the reactor is implemented with one or more optical or contact sensor(s) arranged to measure the temperature of the coated substrates.

In another embodiment, pretreatment is performed by evacuating the ALD reactor. In another embodiment, the evacuating step involves heating in an inert gas atmosphere, such as nitrogen, to cause annealing of the surface.

In one embodiment, in the deposition step, the stack is deposited on the substrate by ALD, as mentioned above and below.

Furthermore, depending on the application, in one embodiment, the applied ALD layer can be additionally coated by a further coating method, for example with a lacquer, for example for improved mechanical durability. In addition, the ALD layer allows for further coating by a dip-coating process (which, if not according to the invention, could harm the PCB structure, for example due to the solvents used), thereby allowing the ALD layer makes the application of such new processes possible. The advantage of ALD alone over other coatings is that since no additional coatings need to be applied, the mass or dimensions of the coated object do not increase significantly, since the ALD layer is typically ~100 nm thick conformally. .

Figure 2 is a schematic diagram of embodiments of a stack deposited on a substrate deposited using the present method. Stacked layers 100, 200, and 300 are deposited on the substrate 10. Layer 100 is at the interface to the substrate, and herein refers to a single deposited material, such as Al ₂ O ₃ . Layer 200 consists of a single layer or sublayers (e.g., I, II, II, III, and IV, or combinations thereof), at least one of which is elastic, or is a carbon, organic material, or silicone polymer. It contains cross-linked chains. In one implementation, layer 200 consists of any number of combinations or repetitions of at least one sublayer I, II, III, and IV.

300 is a surface layer that has the function of protecting against surface chemical reactions such as hydrolysis. Alternatively or additionally, it may contain chemicals adapted to chemically adhere to possible layers of organic matter (such as lacquer) added after the ALD process.

Figure 2 shows a schematic diagram of embodiments of a stack deposited on a substrate deposited using the present method. Stacked layers 100, 200, and 300 are deposited on the substrate 10. Various implementations of the first layer are shown on the left. Layer 200-I is one implementation of layer 200 and illustrates an implementation in which only a single layer of layer I is deposited on the surface. Layer 200-I-II is one implementation of layer 200, where layer 200 is divided into layers I and II, which correspond to sublayers 210 and 220, respectively, as defined above. shows an implementation example formed by (same as). Layer 200-I-II-III is one implementation of layer 200, wherein layer 200 corresponds to layers I, II, and III, which correspond to lower layers 210, 220, and 230, respectively. , as defined above) illustrates an implementation example formed by: In one embodiment, in structures 200-I-II and 200-I-II-III, this layered structure is repeated at least twice (not shown in Figure 2).

When the substrate is a PCB and the method is used during the manufacturing process of the PCB or a device using the same, a layered structure stack is formed on the substrate. The stack provides protection and prevents tin whisker formation on the PCB, improving its quality and resistance to corrosion and damage during use.

Layers 100-300 are deposited in a conventional manner in an ALD reactor. Layers 100, 200 and 300 are deposited by ALD on top of the substrate.

An example of a minimal stack excluding cleaning is:

x (TMA + H ₂ O), where x is the number of cycles required to produce the required layer thickness, at the temperature used (eg x = 1000 at 125°C). This represents layer (I).

Other examples of stacks include:

z { _{_} _ is different and/or greater than 1. This represents layers (I and II). Optionally, layer (II) is anything other than just layer (I).

Another example of a stack is:

z { _{_} _ _ _{_ _} It represents layers II(a), II(b) and III, where the first occurrence of II(a) is in fact layer I.

For clarity, layer 200 may consist of any number of sublayers (II) (e.g., y (TMA+ethylglycol) or stacked x (TMA+H ₂ O) + y (TMA+ethylglycol).

Another example of a stack is a stack in which the Al ₂ O ₃ layer resulting from TMA + H ₂ O is replaced by an oxide (eg, a combination of variations from TiO ₂ to Al ₂ O ₃ + TiO ₂ ). If TiCl ₄ is considered as a precursor for TiO ₂ , the following structures can be produced or:

(TMA + H ₂ O) -> (TMA + H ₂ O) + (TiCl ₄ + H2O)

Alternatively, any combination of structures may be created in the following manner:

z { x (TMA+H ₂ O) + n (TiCl ₄ +H ₂ O) + y (TMA+ethyl glycol) + } + m (TMA+H ₂ O)

where m and n are the same or different and/or greater than 1.

Another example is TMA + ethyl glycol (commonly known as AB), which can be replaced by TMA + ethyl glycol + H ₂ O (ABC), where the added water is intended to react with the unreacted TMA. . Layer (II) may contain AB or ABC.

4A and 4B, according to one embodiment of the first aspect of the invention, an ALD coating made of laminated Al ₂ O ₃ and alucon remains even after 6 months in ambient storage. It can prevent the growth of filament-shaped tin whiskers. The samples were fabricated by electroplating ~2μm SnCu on copper, and these samples were intended to spontaneously generate tin whiskers at accelerated rates. The thickness of the ALD coating was ~500 nm: Al ₂ O ₃ + 19*(Al ₂ O ₃ + alucon) + Al ₂ O ₃ . The ALD coating took place 4 days after the initial metal coating, by which time the structures shown on the left were already visible. This structure implies stacks of 100, 200 and 300, where 100 and 300 are the same material.

In another embodiment, ALD (including MLD and ALE) growth on a PCB is blocked at several locations by depositing only the intended alloy surface (e.g., depositing on the solder but not on the dielectric material). This can be achieved by using specific chemistries and processes. Such targeted deposition can be made possible by blocking growth in undesirable locations (e.g., the dielectric), which can be achieved with the help of chemicals commonly known as ALD growth inhibitors. Growth inhibitors include materials such as self-assembly monolayers of certain silanes. Inside or outside the reactor, the chemistry of this inhibitory coating can be tailored, for example, so that it does not coat the solder. Such specific coatings enable, for example, coating of the solder surface with a thin film of a possibly conductive layer, which in some cases may be desirable to change the surface tension of the solder. Therefore, clearly, if the surface tension can be varied without damaging the electrical surface insulation, the patterning presented herein need not be applied with a mask or marking.

3 shows an ALD reactor system 700, a reactor and its control system according to an example implementation. In one embodiment, an ALD reactor comprises a reaction chamber, in which a substrate (e.g., a PCB, semi-finished assembly, or component board assembly) can be loaded in a suitable manner, for example, the reactor: It can be integrated into a production line, allowing the production line to move through the ALD reactor. The precursor source or sources, in one embodiment, is provided in fluid communication with the reaction chamber of the reactor via an in-feed part. The reaction residue from the reaction chamber can be pumped into the discharge line, ie fore-line, via a vacuum pump. The ALD reactor may be fluidly connected to means for monitoring cleaning between method steps described herein.

In one embodiment, the system includes measurement means 708 configured to indicate sufficient degassing, and/or drying, and/or administration of reactive chemicals to the substrate. In one embodiment, such means include, for example, mass spectrometers and/or optical means, which determine the chemical composition of the gases leaving the reactor, either from within the reactor, from the fore-line, or after the pump. It is configured to measure content or signature or pressure. This system is commonly known as a Residual Gas Analyzer (RGA). In one implementation, RGA 708 is configured to communicate with control means 702 or HMI 706 or a separate user interface to determine the chemical properties of gases from the reactor (or of fore-line 710 gases). Alternatively, it may indicate elemental components or fingerprints and their concentrations. For high quality ALD reactions, it is important, for example, to flush out all reactive gases, for example reduced to less than one part per thousand, more preferably less than 1 PPM. In one implementation, RGA 708 is used to sample all effluent gases from the reaction chamber. In a further embodiment, RGA is used to quantify the quantity and quality of effluent gases under ambient conditions, heating conditions, or chemical exposure conditions of the substrate(s) required in aerospace applications.

In one embodiment, the fore-line 710 includes heating means to substantially prevent or at least significantly reduce the generation of undesirable particles. The heating means is arranged upstream of the vacuum reducing valve in the fore-line 710 in one embodiment.

In one implementation, ALD reactor system 700 includes at least one additional gas inlet configured to be heated separately from the other gas inlets, to a temperature of at least 500° C.

In one embodiment, the at least one additional gas inlet is made of ceramic material, metal, or metal coated with ceramic material.

In one embodiment, at least one additional gas inlet is configured for heating in the intermediate space of the reactor.

In one implementation, ALD reactor system 700 includes gas inlets configured to pulse H ₂ , O ₂ and/or O ₃ .

In one implementation, ALD reactor system 700 includes gas inlets configured to withstand heat above the reaction chamber temperature.

In one implementation, ALD reactor system 700 includes gas inlets configured to enable gas pulses with a temperature difference of at least 100 degrees Celsius compared to the reactor space.

Intermediate space refers to the internal part of the ALD reactor that is rated at a pressure lower than ambient pressure and/or is filled with an inert gas and is further arranged to avoid contact with reactive chemicals. .

The deposition process and reactor system, in one implementation, are controlled by a control system. In one embodiment, the ALD reactor is a computer-controlled system. A computer program stored in the memory of the system includes instructions that, when executed by at least one processor of the system, cause the ALD reactor to operate as directed. The instructions may be in the form of computer-readable program code. In a basic system configuration according to one implementation, process parameters are programmed with the help of software, instructions are executed to a human machine interface (HMI) terminal 706, and control means ( 702). In one implementation, the control means 702 comprises a general purpose programmable logic control (PLC) unit. Control means 702 includes at least one microprocessor for executing control software including program code stored in memory, dynamic and static memory, I/O modules, A/D and D/A converters and power relays. . Control means 702 directs power to a pneumatic controller of the feed input line valve of the ALD reactor and is in bi-directional communication with the feed input line mass flow controller and the precursor source or sources, as well as for operation of the ALD reactor. Perform other controls. Control means 702, in one embodiment, measures readings of probes, sensors or measurement means from the ALD reactor or its gas lines and then relays them to HMI terminal 706. Dashed line 716 represents the interface line between ALD reactor components and control means 702. HMI terminal 706 and control means 702 may be combined as one module.

The inventors have established that the above-described method of combining pretreatment with the deposition of at least one layer by ALD substantially prevents or at least significantly reduces the formation of metal whiskers, especially metal whiskers of the filament type.

Without limiting the scope and interpretation of the patent claims, specific technical effects of one or more of the exemplary embodiments disclosed herein are listed as follows: One technical effect is to prevent the formation of tin whiskers. Another technical benefit is to provide resistance to corrosive chemicals such as water or sulfur. Another technical effect is the prevention of electromigration, which is optionally caused by moisture. Another technical effect is to increase the mechanical strength of ALD layers, such as hard ALD layers. Another technical effect is the protection of conductive materials from which tin whisker formation is possible. Another technical effect is protection against gas corrosion. Another technological effect is to provide a low-cost manufacturing process. Another technical effect is that the laminated stack can be opened for reprocessing, such as connection or contact, for example by laser.

The methods and tools provided herein enable the formation of a corrosion barrier against corrosive gases, moisture, liquids (depending on the coating used, e.g. water), while simultaneously mitigating tin whiskers. Additionally, the method allows protection against electromigration, known as dendrite formation.

Additionally, the provided method prevents corrosion of the PCB surface, most often associated with liquids, condensates or humid air on metal surfaces.

Additionally, the main advantage of using ALD in PCBs to alleviate the tin whisker problem is that the ALD layer can be reprocessed in the repair process, for example by removing the coating mechanically or with a laser. Additionally, because the ALD layer between the solder beneath the ADL and potential additional components (e.g., solder paste) can effectively strip away hard insulating materials, ALD coatings can be used to attach components over soldered parts. It is possible.

Another advantage of the invention is that, for example, if the component legs are not coated, they are protected from tin whiskers, corrosion, electrical breakthrough, or electromigration, for example through the surrounding environment. It becomes possible to protect the target component or board, possibly with components, referred to herein as PCB.

Additionally, undercoating of Ball Grid Array (BGA) components is possible with ALD, which is not possible with other protection methods due to the very high aspect ratio.

The foregoing description, by way of non-limiting examples of specific implementations and examples of the invention, has provided a detailed and informative description of the best mode currently contemplated by the inventors for carrying out the invention. However, as will be apparent to those skilled in the art, the present invention is not limited to the details of the embodiments presented above, and may be practiced in other embodiments using equivalent means without departing from the characteristics of the invention. there is.

Additionally, some of the features of the previously described implementations of the invention may be used to gain advantage without corresponding use of other features. As such, the foregoing description should be regarded as merely illustrative of the principles of the invention and should not be considered as limiting the principles of the invention. Accordingly, the scope of the present invention is limited only by the appended claims.

Claims (34)

1. A deposition method performed in a reactor system to reduce metal whisker formation, electromigration and corrosion, comprising:
providing a substrate;
Pretreating the substrate by washing;
pretreating the substrate by preheating or evacuating; and
A stack deposition step comprising depositing at least the first layer 100 by atomic layer deposition (ALD),
The stack deposition step includes a first pulse with at least one reductive chemical,
During the stack deposition step, reactive gas is pumped from the reaction chamber to the exhaust fore-line, reaching an amount of less than one part per thousand,
The reactive gas in the discharge fore-line is analyzed by a residual gas analyzer,
the residual gas analyzer is connected to control means for controlling the operation of the reactor system,
The stack deposition step further includes depositing a second layer 200 composed of different sublayers by atomic layer deposition (ALD), wherein the second layer 200 includes at least one organic A deposition method comprising a sublayer or a silicon polymer containing sublayer. In claim 1,
A method of deposition, wherein the first pulse consists of a reductive chemical or multiple pulses of chemicals with subsequent inert gas pulses therebetween. In claim 1,
The deposition method of claim 1, wherein the metal includes Zn, Sn, Cd or Ag. In claim 1,
A deposition method in which filament type metal whisker formation is reduced or prevented. In claim 1,
The substrate may include a printed circuit board (PCB); component; Component housing; or a metal housing; a deposition method comprising: In claim 1,
The method of claim 1 , wherein the second layer (200) consists of at least one elastic sublayer. In claim 1,
The second layer (200) includes at least one sublayer of electrically insulating material. In claim 1,
The method of claim 1 , wherein the stack includes at least one sublayer that is a hard layer. In claim 1,
The deposition method further includes depositing the third layer 300 by atomic layer deposition (ALD). In claim 1,
The method of claim 1 , wherein pretreating the substrate by preheating includes preheating the substrate with a pulse of heated gas having a temperature above the reaction temperature. In claim 1,
A method of deposition, wherein at least one layer includes at least one reactive chemical that is reactive with the ambient. In claim 1,
The deposition method of claim 1, wherein the stack has a thickness of 1 to 2000 nm. In claim 1,
A method of deposition, further comprising altering, stopping or limiting said exhaust fore-line flow. In claim 1,
The deposition method further comprising providing an additional coating on top of the stack by an additional coating method. In claim 14,
The method of claim 1 , wherein the additional coating comprises a lacquer-like polymer or a silicone polymer. In claim 1,
The method of claim 1 , wherein the cleaning comprises an ALE pulse. In claim 1,
The method of claim 1 , wherein the cleaning comprises using heated H ₂ or O ₂ or O ₃ . The method of any one of claims 1 to 17,
The deposition method is used to protect the substrate from metal whisker formation, electromigration and/or corrosion. An ALD reactor system (700) comprising control means (702) configured to cause the ALD reactor system to perform the deposition method of any one of claims 1-17, wherein the ALD reactor system:
a reactor chamber in fluid communication with a fore-line, vacuum pump and residual gas analyzer;
first pre-treatment means configured to pre-treat the substrate by washing;
a second pre-treatment means configured to pre-treat the substrate by preheating;
stack deposition means comprising depositing at least a first layer (100) on the substrate by atomic layer deposition (ALD); and
a heated gas exhaust fore-line having means for changing the flow of heated gas;
wherein the residual gas analyzer is configured to communicate with control means,
The stack deposition means deposits, by atomic layer deposition (ALD), a second layer 200 consisting of different sublayers, the second layer 200 containing at least one organic sublayer or a silicon polymer. ALD reactor system 700 consisting of a sub-layer. In claim 19,
ALD reactor system 700 further comprising at least one additional gas inlet configured to be heated separately from the other gas inlets to a temperature of at least 500° C. In claim 19,
An ALD reactor system (700) comprising a gas inlet configured to enable pulsing of H ₂ , O ₂ or O ₃ . In claim 19,
An ALD reactor system 700 including a gas inlet configured to withstand heat above the reaction chamber temperature. In claim 19,
An ALD reactor system (700) comprising a gas inlet configured to enable gas pulses with a temperature difference of at least 100° C. compared to the space of the reactor chamber. In claim 20,
ALD reactor system (700), wherein the at least one additional gas inlet is made of ceramic material or metal, or metal coated with ceramic material. In claim 20,
An ALD reactor system (700), wherein the at least one additional gas inlet is configured to heat an intermediate space of the reactor. delete delete delete delete delete delete delete delete delete